There has been considerable study of various network interconnection topologies. In particular, a paper entitled "Communication Structures for Large Networks of Microcomputers" by L. D. Wittie, IEEE Transactions on Computers, Vol. C-30, #4, April 1981 pps. 264-273, describes a variety of electrical interconnection networks that are deemed especially useful for interconnecting a large number of processing elements.
Currently, there is increasing interest in optical interconnection networks because of the fast transfers, large bandwidth and non-interfering free-space propagation that such networks promise. A reconfigurable optical interconnect, such as a completely-connected cross-bar, was expected to be of special interest because its non-blocking communication structure is capable of providing a large degree of routing flexibility with a short reconfiguration time. It appears, however, that the routing flexibility of a cross-bar with N processing elements is offset by its serious energy drawback, e.g. a power distribution loss (PDL) proportional to N. Based on this fundamental limit, it is expected that a cross-bar can only be efficiently implemented for a moderate value of N, say less than 1000. A second major difficulty for an optical cross-bar has been the lack of efficient optical components for a two-dimensional array implementation, so that the tendency has been to put N processing elements along a linear array.
The Mesh-Connected-Bus (MCB) network topology used in the invention may be viewed as a two-dimensional example of Wittie's D-dimensional hypercube bus family networks, and Wittie has pointed out that such networks have a connectivity of .sqroot.N and are amenable to non-blocking switching in three routing steps. A subsequent paper entitled "Wavelength Division Multiple Access Channel Hypercube Processor Interconnection" IEEE Transitions on Computers VOL C-41, pps. 1223-1241, (1992) proposes a fiber optical architecture to implement such a network but such an architecture becomes very complex when a large number of processing elements are to be interconnected.